So, I want to use the pretrained models to feature extract features from images, so I used “resnet50 , incepton_v3, Xception, inception_resnet” models, removed the classifier or FC depends on the model architecture, as some models have model.fc and other have model.classifier and other have model.classi , then I concatenated the features and trained the concatenated features in a deep neural network, but I got validation accuracy 1% only, although when I did the same network in Tensorflow I got accuracy of 95%, so can someone clarify what I did wrong in my pytorch notebook?
model_resnet = models.resnet50(pretrained=True).cuda()
model_resnet.fc=nn.Sequential()
model_incep = models.inception_v3 (pretrained=True).cuda()
model_incep.fc=nn.Sequential()
model_xcep = timm.create_model(‘xception’, pretrained=True).cuda()
model_xcep.fc=nn.Sequential()
model_incep_res = timm.create_model(‘ens_adv_inception_resnet_v2’, pretrained=True).cuda()
model_incep_res.classif=nn.Sequential()
def features_extract(loader, model,features):
num_correct = 0
num_samples = 0
model.eval()
i=0
batchsize=64
score=torch.empty((10222,features))
with torch.no_grad():
for x, y in iter(loader):
x = x.to(device=device)
y = y.to(device=device)
scores = model(x)
score[i*64:(i+1)*64]=scores
i+=1
model.train()
return score
score_res=features_extract(trainloader,model_resnet,2048)
score_incep=features_extract(trainloader,model_incep,2048)
score_incep_res=features_extract(trainloader,model_incep_res,1536)
score_xcep=features_extract(trainloader,model_xcep,2048)
features_extracted=torch.cat([score_res,score_incep,score_incep_res,score_xcep],axis=1)
from collections import OrderedDict
my_model=nn.Sequential(OrderedDict([(‘fc1’, nn.Linear(7680, 5000)),
(‘drop’, nn.Dropout(p=0.5)),
(‘fc2’, nn.Linear(5000, 120)),
(‘output’, nn.Softmax(dim=0))])).cuda()
criterion = nn.CrossEntropyLoss()
optimizer = optim.Adam(my_model.parameters(), 0.001 )
from tqdm import tqdm
epochs = 5
check_every = 1
iters = 0
train_loss=0
modle.to(device)
from tqdm import tqdm
epochs = 5
check_every = 1
iters = 0
train_loss=0
modle.to(device)
for epoch in range(epochs):
for i in range(features_extracted.shape[0]):
# Get data to cuda if possible
data = features_extracted[i].to(device=device)
targets = y_train[i].to(device=device)
# forward
scores = modle(torch.reshape(data,(-1,7680)))
scores=max(scores)
loss = criterion(scores, targets)
# backward
optimizer.zero_grad()
loss.backward()
# gradient descent or adam step
optimizer.step()
def check_accuracy(features_extracted, model,y_train):
num_correct = 0
num_samples = 0
model.eval()
with torch.no_grad():
for i in range(features_extracted.shape[0]):
# Get data to cuda if possible
data = features_extracted[i].to(device=device)
targets = y_train[i].to(device=device)
global scores
scores = model(data)
predictions = torch.argmax(scores)
if(predictions==y_train[i]):
num_correct+=1
model.train()
return num_correct/features_extracted.shape[0]
print(f"Accuracy on Validation set: {check_accuracy(features_val, modle,y_val):.2f}")
I followed Aladdin Persson's Youtube video to code up just the encoder portion of the transformer model in PyTorch, except I just used the Pytorch's multi-head attention layer. The model seems to produce the correct shape of data. However, during training, the training loss does not drop and the resulting model always predicts the same output of 0.4761. Dataset used for training is from the Sarcasm Detection Dataset from Kaggle. Would appreciate any help you guys can give on errors that I have made.
import pandas as pd
from transformers import BertTokenizer
import torch.nn as nn
import torch
from sklearn.model_selection import train_test_split
from torch.optim.lr_scheduler import ReduceLROnPlateau
import math
df = pd.read_json("Sarcasm_Headlines_Dataset_v2.json", lines=True)
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
encoded_input = tokenizer(df['headline'].tolist(), return_tensors='pt',padding=True)
X = encoded_input['input_ids']
y = torch.tensor(df['is_sarcastic'].values).float()
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42, stratify = y)
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
print(device)
torch.cuda.empty_cache()
class TransformerBlock(nn.Module):
def __init__(self,embed_dim, num_heads, dropout, expansion_ratio):
super(TransformerBlock, self).__init__()
self.attention = nn.MultiheadAttention(embed_dim, num_heads)
self.norm1 = nn.LayerNorm(embed_dim)
self.norm2 = nn.LayerNorm(embed_dim)
self.feed_forward = nn.Sequential(
nn.Linear(embed_dim, expansion_ratio*embed_dim),
nn.ReLU(),
nn.Linear(expansion_ratio*embed_dim,embed_dim)
)
self.dropout = nn.Dropout(dropout)
def forward(self, value, key, query):
attention, _ = self.attention(value, key, query)
x=self.dropout(self.norm1(attention+query))
forward = self.feed_forward(x)
out=self.dropout(self.norm2(forward+x))
return out
class Encoder(nn.Module):
#the vocab size is one more than the max value in the X matrix.
def __init__(self,vocab_size=30109,embed_dim=128,num_layers=1,num_heads=4,device="cpu",expansion_ratio=4,dropout=0.1,max_length=193):
super(Encoder,self).__init__()
self.device = device
self.word_embedding = nn.Embedding(vocab_size,embed_dim)
self.position_embedding = nn.Embedding(max_length,embed_dim)
self.layers = nn.ModuleList(
[
TransformerBlock(embed_dim,num_heads,dropout,expansion_ratio) for _ in range(num_layers)
]
)
self.dropout = nn.Dropout(dropout)
self.classifier1 = nn.Linear(embed_dim,embed_dim)
self.classifier2 = nn.Linear(embed_dim,1)
self.relu = nn.ReLU()
def forward(self,x):
N, seq_length = x.shape
positions = torch.arange(0,seq_length).expand(N, seq_length).to(self.device)
out = self.dropout(self.word_embedding(x) + self.position_embedding(positions))
for layer in self.layers:
#print(out.shape)
out = layer(out,out,out)
#Get the first output for classification
#Pooled output from hugging face is: Last layer hidden-state of the first token of the sequence (classification token) further processed by a Linear layer and a Tanh activation function.
#Pooled output from hugging face will be different from out[:,0,:], which is the output from the CLS token.
out = self.relu(self.classifier1(out[:,0,:]))
out = self.classifier2(out)
return out
torch.cuda.empty_cache()
net = Encoder(device=device)
net.to(device)
batch_size = 32
num_train_samples = X_train.shape[0]
num_val_samples = X_test.shape[0]
criterion = nn.BCEWithLogitsLoss()
optimizer = torch.optim.Adam(net.parameters(),lr=1e-5)
scheduler = ReduceLROnPlateau(optimizer, 'min', patience=5)
val_loss_hist=[]
loss_hist=[]
epoch = 0
min_val_loss = math.inf
print("Training Started")
patience = 0
for _ in range(100):
epoch += 1
net.train()
epoch_loss = 0
permutation = torch.randperm(X_train.size()[0])
for i in range(0,X_train.size()[0], batch_size):
indices = permutation[i:i+batch_size]
features=X_train[indices].to(device)
labels=y_train[indices].reshape(-1,1).to(device)
output = net.forward(features)
loss = criterion(output, labels)
optimizer.zero_grad()
loss.backward()
optimizer.step()
epoch_loss+=loss.item()
epoch_loss = epoch_loss / num_train_samples * num_val_samples
loss_hist.append(epoch_loss)
#print("Eval")
net.eval()
epoch_val_loss = 0
permutation = torch.randperm(X_test.size()[0])
for i in range(0,X_test.size()[0], batch_size):
indices = permutation[i:i+batch_size]
features=X_test[indices].to(device)
labels = y_test[indices].reshape(-1,1).to(device)
output = net.forward(features)
loss = criterion(output, labels)
epoch_val_loss+=loss.item()
val_loss_hist.append(epoch_val_loss)
scheduler.step(epoch_val_loss)
#if epoch % 5 == 0:
print("Epoch: " + str(epoch) + " Train Loss: " + format(epoch_loss, ".4f") + ". Val Loss: " + format(epoch_val_loss, ".4f") + " LR: " + str(optimizer.param_groups[0]['lr']))
if epoch_val_loss < min_val_loss:
min_val_loss = epoch_val_loss
torch.save(net.state_dict(), "torchmodel/weights_best.pth")
print('\033[93m'+"Model Saved"+'\033[0m')
patience = 0
else:
patience += 1
if (patience == 10):
break
print("Training Ended")
I've trained a vgg16 model to predict 102 classes of flowers.
It works however now that I'm trying to understand one of it's predictions I feel it's not acting normally.
model layout
# Imports here
import os
import numpy as np
import torch
import torchvision
from torchvision import datasets, models, transforms
import matplotlib.pyplot as plt
import json
from pprint import pprint
from scipy import misc
%matplotlib inline
data_dir = 'flower_data'
train_dir = data_dir + '/train'
test_dir = data_dir + '/valid'
json_data=open('cat_to_name.json').read()
main_classes = json.loads(json_data)
main_classes = {int(k):v for k,v in classes.items()}
train_transform_2 = transforms.Compose([transforms.RandomResizedCrop(224),
transforms.RandomRotation(30),
transforms.RandomHorizontalFlip(),
transforms.ToTensor()])
test_transform_2= transforms.Compose([transforms.RandomResizedCrop(224),
transforms.ToTensor()])
# TODO: Load the datasets with ImageFolder
train_data = datasets.ImageFolder(train_dir, transform=train_transform_2)
test_data = datasets.ImageFolder(test_dir, transform=test_transform_2)
# define dataloader parameters
batch_size = 20
num_workers=0
# TODO: Using the image datasets and the trainforms, define the dataloaders
train_loader = torch.utils.data.DataLoader(train_data, batch_size=batch_size,
num_workers=num_workers, shuffle=True)
test_loader = torch.utils.data.DataLoader(test_data, batch_size=batch_size,
num_workers=num_workers, shuffle=True)
vgg16 = models.vgg16(pretrained=True)
# Freeze training for all "features" layers
for param in vgg16.features.parameters():
param.requires_grad = False
import torch.nn as nn
n_inputs = vgg16.classifier[6].in_features
# add last linear layer (n_inputs -> 102 flower classes)
# new layers automatically have requires_grad = True
last_layer = nn.Linear(n_inputs, len(classes))
vgg16.classifier[6] = last_layer
import torch.optim as optim
# specify loss function (categorical cross-entropy)
criterion = nn.CrossEntropyLoss()
# specify optimizer (stochastic gradient descent) and learning rate = 0.001
optimizer = optim.SGD(vgg16.classifier.parameters(), lr=0.001)
pre_trained_model=torch.load("model.pt")
new=list(pre_trained_model.items())
my_model_kvpair=vgg16.state_dict()
count=0
for key,value in my_model_kvpair.items():
layer_name, weights = new[count]
my_model_kvpair[key] = weights
count+=1
# number of epochs to train the model
n_epochs = 6
# initialize tracker for minimum validation loss
valid_loss_min = np.Inf # set initial "min" to infinity
for epoch in range(1, n_epochs+1):
# keep track of training and validation loss
train_loss = 0.0
valid_loss = 0.0
###################
# train the model #
###################
# model by default is set to train
vgg16.train()
for batch_i, (data, target) in enumerate(train_loader):
# clear the gradients of all optimized variables
optimizer.zero_grad()
# forward pass: compute predicted outputs by passing inputs to the model
output = vgg16(data)
# calculate the batch loss
loss = criterion(output, target)
# backward pass: compute gradient of the loss with respect to model parameters
loss.backward()
# perform a single optimization step (parameter update)
optimizer.step()
# update training loss
train_loss += loss.item()
if batch_i % 20 == 19: # print training loss every specified number of mini-batches
print('Epoch %d, Batch %d loss: %.16f' %
(epoch, batch_i + 1, train_loss / 20))
train_loss = 0.0
######################
# validate the model #
######################
vgg16.eval() # prep model for evaluation
for data, target in test_loader:
# forward pass: compute predicted outputs by passing inputs to the model
output = vgg16(data)
# calculate the loss
loss = criterion(output, target)
# update running validation loss
valid_loss += loss.item()
# print training/validation statistics
# calculate average loss over an epoch
train_loss = train_loss/len(train_loader.dataset)
valid_loss = valid_loss/len(test_loader.dataset)
print('Epoch: {} \tTraining Loss: {:.6f} \tValidation Loss: {:.6f}'.format(
epoch+1,
train_loss,
valid_loss
))
# save model if validation loss has decreased
if valid_loss <= valid_loss_min:
print('Validation loss decreased ({:.6f} --> {:.6f}). Saving model ...'.format(
valid_loss_min,
valid_loss))
torch.save(vgg16.state_dict(), 'model.pt')
valid_loss_min = valid_loss
testing on a single image
tensor = torch.from_numpy(test_image)
reshaped = tensor.permute(2, 0, 1).unsqueeze(0)
floatified = reshaped.to(torch.float32) / 255
vgg16(floatified)
>>>
tensor([[ 2.5686, -1.1964, -0.0872, -1.7010, -1.6669, -1.0638, 0.4515, 0.1124,
0.0166, 0.3156, 1.1699, 1.5374, 1.8720, 2.5184, 2.9046, -0.8241,
-1.1949, -0.5700, 0.8692, -1.0485, 0.0390, -1.3783, -3.4632, -0.0143,
1.0986, 0.2667, -1.1127, -0.8515, 0.7759, -0.7528, 1.6366, -0.1170,
-0.4983, -2.6970, 0.7545, 0.0188, 0.1094, 0.5002, 0.8838, -0.0006,
-1.7993, -1.3706, 0.4964, -0.3251, -1.7313, 1.8731, 2.4963, 1.1713,
-1.5726, 1.5476, 3.9576, 0.7388, 0.0228, 0.3947, -1.7237, -1.8350,
-2.0297, 1.4088, -1.3469, 1.6128, -1.0851, 2.0257, 0.5881, 0.7498,
0.0738, 2.0592, 1.8034, -0.5468, 1.9512, 0.4534, 0.7746, -1.0465,
-0.7254, 0.3333, -1.6506, -0.4242, 1.9529, -0.4542, 0.2396, -1.6804,
-2.7987, -0.6367, -0.3599, 1.0102, 2.6319, 0.8305, -1.4333, 3.3043,
-0.4021, -0.4877, 0.9125, 0.0607, -1.0326, 1.3186, -2.5861, 0.1211,
-2.3177, -1.5040, 1.0416, 1.4008, 1.4225, -2.7291]],
grad_fn=<ThAddmmBackward>)
sum([ 2.5686, -1.1964, -0.0872, -1.7010, -1.6669, -1.0638, 0.4515, 0.1124,
0.0166, 0.3156, 1.1699, 1.5374, 1.8720, 2.5184, 2.9046, -0.8241,
-1.1949, -0.5700, 0.8692, -1.0485, 0.0390, -1.3783, -3.4632, -0.0143,
1.0986, 0.2667, -1.1127, -0.8515, 0.7759, -0.7528, 1.6366, -0.1170,
-0.4983, -2.6970, 0.7545, 0.0188, 0.1094, 0.5002, 0.8838, -0.0006,
-1.7993, -1.3706, 0.4964, -0.3251, -1.7313, 1.8731, 2.4963, 1.1713,
-1.5726, 1.5476, 3.9576, 0.7388, 0.0228, 0.3947, -1.7237, -1.8350,
-2.0297, 1.4088, -1.3469, 1.6128, -1.0851, 2.0257, 0.5881, 0.7498,
0.0738, 2.0592, 1.8034, -0.5468, 1.9512, 0.4534, 0.7746, -1.0465,
-0.7254, 0.3333, -1.6506, -0.4242, 1.9529, -0.4542, 0.2396, -1.6804,
-2.7987, -0.6367, -0.3599, 1.0102, 2.6319, 0.8305, -1.4333, 3.3043,
-0.4021, -0.4877, 0.9125, 0.0607, -1.0326, 1.3186, -2.5861, 0.1211,
-2.3177, -1.5040, 1.0416, 1.4008, 1.4225, -2.7291])
>>>
5.325799999999998
given this as how I test it on a single image (and the model as usual is trained and tested on batches it returns a prediction matrix that doesn't seem to be normalized or add up to 1.
Is this normal?
Yes, official network implementations in PyTorch don't apply softmax to the last linear layer. Check the code for VGG. You can use nn.softmax to achieve what you want:
m = nn.Softmax()
out = vgg16(floatified)
out = m(out)
You can also use nn.functional.softmax:
out = nn.functional.softmax(vgg16(floatified))
I am using PyTorch to train a cnn model. Here is my Network architecture:
import torch
from torch.autograd import Variable
import torch.nn as nn
import torch.nn.functional as F
import torch.nn.init as I
class Net(nn.Module):
def __init__(self):
super(Net, self).__init__()
self.conv1 = nn.Conv2d(1, 32, 5)
self.pool = nn.MaxPool2d(2,2)
self.conv1_bn = nn.BatchNorm2d(32)
self.conv2 = nn.Conv2d(32, 64, 5)
self.conv2_drop = nn.Dropout2d()
self.conv2_bn = nn.BatchNorm2d(64)
self.fc1 = torch.nn.Linear(53*53*64, 256)
self.fc2 = nn.Linear(256, 136)
def forward(self, x):
x = F.relu(self.conv1_bn(self.pool(self.conv1(x))))
x = F.relu(self.conv2_bn(self.pool(self.conv2_drop(self.conv2(x)))))
x = x.view(-1, 53*53*64)
x = F.relu(self.fc1(x))
x = F.dropout(x, training=self.training)
x = self.fc2(x)
return x
Then I train the model like below:
# prepare the net for training
net.train()
for epoch in range(n_epochs): # loop over the dataset multiple times
running_loss = 0.0
# train on batches of data, assumes you already have train_loader
for batch_i, data in enumerate(train_loader):
# get the input images and their corresponding labels
images = data['image']
key_pts = data['keypoints']
# flatten pts
key_pts = key_pts.view(key_pts.size(0), -1)
# wrap them in a torch Variable
images, key_pts = Variable(images), Variable(key_pts)
# convert variables to floats for regression loss
key_pts = key_pts.type(torch.FloatTensor)
images = images.type(torch.FloatTensor)
# forward pass to get outputs
output_pts = net(images)
# calculate the loss between predicted and target keypoints
loss = criterion(output_pts, key_pts)
# zero the parameter (weight) gradients
optimizer.zero_grad()
# backward pass to calculate the weight gradients
loss.backward()
# update the weights
optimizer.step()
# print loss statistics
running_loss += loss.data[0]
I am wondering if it is possible to add the validation error in the training? I mean something like this (validation split) in Keras:
myModel.fit(trainX, trainY, epochs=50, batch_size=1, verbose=2, validation_split = 0.1)
Here is an example how to split your dataset for training and validation, then switch between the two phases every epoch:
import numpy as np
import torch
from torchvision import datasets
from torch.autograd import Variable
from torch.utils.data.sampler import SubsetRandomSampler
# Examples:
my_dataset = datasets.MNIST(root="/home/benjamin/datasets/mnist", train=True, download=True)
validation_split = 0.1
dataset_len = len(my_dataset)
indices = list(range(dataset_len))
# Randomly splitting indices:
val_len = int(np.floor(validation_split * dataset_len))
validation_idx = np.random.choice(indices, size=val_len, replace=False)
train_idx = list(set(indices) - set(validation_idx))
# Contiguous split
# train_idx, validation_idx = indices[split:], indices[:split]
## Defining the samplers for each phase based on the random indices:
train_sampler = SubsetRandomSampler(train_idx)
validation_sampler = SubsetRandomSampler(validation_idx)
train_loader = torch.utils.data.DataLoader(my_dataset, sampler=train_sampler)
validation_loader = torch.utils.data.DataLoader(my_dataset, sampler=validation_sampler)
data_loaders = {"train": train_loader, "val": validation_loader}
data_lengths = {"train": len(train_idx), "val": val_len}
# Training with Validation (your code + code from Pytorch tutorial: https://pytorch.org/tutorials/beginner/transfer_learning_tutorial.html)
n_epochs = 40
net = ...
for epoch in range(n_epochs):
print('Epoch {}/{}'.format(epoch, n_epochs - 1))
print('-' * 10)
# Each epoch has a training and validation phase
for phase in ['train', 'val']:
if phase == 'train':
optimizer = scheduler(optimizer, epoch)
net.train(True) # Set model to training mode
else:
net.train(False) # Set model to evaluate mode
running_loss = 0.0
# Iterate over data.
for data in data_loaders[phase]:
# get the input images and their corresponding labels
images = data['image']
key_pts = data['keypoints']
# flatten pts
key_pts = key_pts.view(key_pts.size(0), -1)
# wrap them in a torch Variable
images, key_pts = Variable(images), Variable(key_pts)
# convert variables to floats for regression loss
key_pts = key_pts.type(torch.FloatTensor)
images = images.type(torch.FloatTensor)
# forward pass to get outputs
output_pts = net(images)
# calculate the loss between predicted and target keypoints
loss = criterion(output_pts, key_pts)
# zero the parameter (weight) gradients
optimizer.zero_grad()
# backward + optimize only if in training phase
if phase == 'train':
loss.backward()
# update the weights
optimizer.step()
# print loss statistics
running_loss += loss.data[0]
epoch_loss = running_loss / data_lengths[phase]
print('{} Loss: {:.4f}'.format(phase, epoch_loss))
I am training the skipgram word embeddings using the famous model described in https://arxiv.org/abs/1310.4546. I want to train it in PyTorch but I am getting errors and I can't figure out where they are coming from. Below I have provided my model class, training loop, and batching method. Does anyone have any insight into whats going on?
I am getting an error on the output = loss(data, target) line. It is having a problem with <class 'torch.LongTensor'> which is weird because CrossEntropyLoss takes a long tensor. The output shape might be wrong which is: torch.Size([1000, 100, 1000]) after the feedforward.
I have my model defined as:
import torch
import torch.nn as nn
torch.manual_seed(1)
class SkipGram(nn.Module):
def __init__(self, vocab_size, embedding_dim):
super(SkipGram, self).__init__()
self.embeddings = nn.Embedding(vocab_size, embedding_dim)
self.hidden_layer = nn.Linear(embedding_dim, vocab_size)
# Loss needs to be input: (minibatch (N), C) target: (minibatch, 1), each label is a class
# Calculate loss in training
def forward(self, x):
embeds = self.embeddings(x)
x = self.hidden_layer(embeds)
return x
My training is defined as:
import torch.optim as optim
from torch.autograd import Variable
net = SkipGram(1000, 300)
optimizer = optim.SGD(net.parameters(), lr=0.01)
batch_size = 100
size = len(train_ints)
batches = batch_index_gen(batch_size, size)
inputs, targets = build_tensor_from_batch_index(batches[0], train_ints)
for i in range(100):
running_loss = 0.0
for batch_idx, batch in enumerate(batches):
data, target = build_tensor_from_batch_index(batch, train_ints)
# if (torch.cuda.is_available()):
# data, target = data.cuda(), target.cuda()
# net = net.cuda()
data, target = Variable(data), Variable(target)
optimizer.zero_grad()
output = net.forward(data)
loss = nn.CrossEntropyLoss()
output = loss(data, target)
output.backward()
optimizer.step()
running_loss += loss.data[0]
optimizer.step()
print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}'.format(
i, batch_idx * len(batch_size), len(size),
100. * (batch_idx * len(batch_size)) / len(size), loss.data[0]))
If useful my batching is:
def build_tensor_from_batch_index(index, train_ints):
minibatch = []
for i in range(index[0], index[1]):
input_arr = np.zeros( (1000,1), dtype=np.int )
target_arr = np.zeros( (1000,1), dtype=np.int )
input_index, target_index = train_ints[i]
input_arr[input_index] = 1
target_arr[input_index] = 1
input_tensor = torch.from_numpy(input_arr)
target_tensor = torch.from_numpy(target_arr)
minibatch.append( (input_tensor, target_tensor) )
# Concatenate all tensors into a minibatch
#x = [tensor[0] for tensor in minibatch]
#print(x)
input_minibatch = torch.cat([tensor[0] for tensor in minibatch], 1)
target_minibatch = torch.cat([tensor[1] for tensor in minibatch], 1)
#target_minibatch = minibatch[0][1]
return input_minibatch, target_minibatch
I'm not sure about that since I did not read the paper, but seems weird that you are computing the loss with the original data and the targets:
output = loss(data, target)
Considering that the output of the network is output = net.forward(data) I think you should compute your loss as:
error = loss(output, target)
If this doesn't help, briefly point me out what the paper says about the loss function.